freelancing while you have a full-time job

I work for a national trade magazine and freelance for local papers and magazines as a second job (since magazine editors don't pay much to start with). I've been doing it for more than five years. Recently, however, my boss started a subscription to a local magazine and saw one of my articles. He called me into his office, yelled a lot, took it pretty personally and threatened to put me on 90-day probation and possibly fire me. By the end of the meeting, he told me I was not on probation and he said he had a letter to give me outlining the topic. I never received a letter and currently don't know whether I'm on probation or not.
I never signed a form saying freelancing was not permitted while working here. Our company manual does include the following statement, but I took it more as I can't freelance for competing magazines in the same industry and not magazines that were unrelated to the industry or category in which this magazine belongs. Please help me decipher the following manual rule and let me know if I can continue to freelance. I feel that I have a rite to hold a second job - others in this company do. It's just when they freelance graphically, their name isn't on it like mine is editorially. Also, the other option is using a pen name to freelance. Are there rules associated with this? Thanks for your help.
Here's the company manual rule on "Outside Employment":
"The company does not want to control the personal affairs of its employees beyond work responsibilities. However, if an employee holds a second job in addition to working for this company, this employment should not conflict with their ability to meet their responsibilities at this company. Likewise, it should be understood that second jobs or work assignments should not, in any way, be in conflict with the principle responsibility at this company (i.e. editors and graphics staff should not be editing, illustrating, writing, nor should sales personnel be selling or in any way supporting magazines, newsletters, associations, or any groups or businesses that are in any way associated with the market in which they have a job responsibility at this company.)
The management of this company views individual entrepreneural media enterprises as conflict of interest, regardless of market served or the nature of content. Likewise, it is viewed as a conflict of interest for artists to freelance art works for other publishers, regardless of market, nor is it acceptable for advertising sales personnel to be involved in any sales marketing activities related to media enterprises."

Also, here is the company's probationary rule:
"Discipline steps include 1. a verbal warning (i.e. discussion of the problem). A written report of the discussion is placed in the employee's personnel file. 2. A written letter reviewing the problem will be presented in a face-to-face meeting with the employee. A copy of the letter and written report of the discussion that takes place in the meeting is placed in the employee's personnel file. 3. A written notice and punitive action, which will be in the way of a determination of a period of probation for the individual involved. Probation period may range from one week to several months as determined by the immediate supervisor involved.
These steps will be invoked in areas such as, but not limited to, tardiness, absenteeism, non-serious horseplay, quality issues, failure to follow rules and/or procedures, non-serious disruption of work environment, poor job performance, smoking policies, etc.
Steps one through three will ususally occur before discharge, however there may be occasions where immediate termination is necessary. The management of this company reserves the right to discipline or discharge any employee at any time for any infraction whether or not it is listed specifically in this book."