Religion is a hot button issue.
It is a polarizing issue along with: Health care. Evolution. Creationism. Welfare. Sexual orientation. Gender roles. Abortion. Politics. Right to bear arms.
There is a reason, like with politics, you shouldn't bring up these issues if you are unsure of your audience -that is, don't bring up these issues if you have any expectation what-so-ever of keeping the conversation on topic. Such as football.
Mentioning, even with the best of intentions, anything about any hot button issue and you only have yourself to blame for where the conversation goes from there. Doing so and then claiming you are "under attack" is passive aggressiveness.
Had you brought up politics or any other hot button issue, you'd have received a similar response from the same kind of people asking you to refrain. Calling them "Christian bigots" for doing so might be correct in some cases but it is also passive-aggressiveness.
I admire the strength of courage it takes Jehovah Witnesses to come knocking on my door. That doesn't mean I want them doing so when I'm watching the game.
I personally dont mind people interjecting references to God in conversations when I can assess that they mean well.. and I know you meant well.. But then, Republicans also mean well, and Democrats also mean well and yet all three are still hot button issues.
Talking about either political party is just going to derail any other conversation. There's a reason I pick and choose my time to talk politics... just as there's a reason we don't see Harry Boy over here talking football. Thank God for that..
(oops).
EDIT: In retrospect, I wish I had used the word "naive" rather than "passive aggressive".. a phrase that I don't think has ever been used in an actually constructive manner in the history of it being in existence.