Could it be that he would have considered attending the service would be praying to a false God?
Only if while attending he actually prayed to the false god. But attending the service for any other reason than worship wouldn't qualify.
He wasn't being exposed to it he was required to go to a religious service.
Sort of, but not really. He wasn't being required to go to a service, he was being required to go to an event where they was
also going to be a service. The service wasn't the primary reason for him going, nor the primary reason for inviting the police.
If I understood correctly it wasn't the normal cake and cookies appreciation day event, it was piggy backed on to their normal religious service.
Well no, not really. It was, literally, a "law enforcement appreciation day" held in appreciation for the work the Tulsa PD did in relation to the mosque. They also scheduled the "appreciation day" on a day when religious services would take place, not because they wanted to worship with a bunch of infidels (and certainly not to proselytize and convert any of them, since that's quite impossible according to the Qur'an anyway - which office Fields would have known had he bothered to learn anything about Muslims), but because they wanted to show the police department what they do, what they were all about, to take the opportunity to dispel misunderstandings and prejudices.
If this article was more balanced it would have said that the officer was required to attend a religious service.
Actually that wouldn't be balanced at all. The WND piece is already slanted and very selective with it's facts and conclusions as it is. No point in going overboard with it.