A fork most certainly could have happened because of the BU and SPV miners.
As I said, not in any real way, it couldn't.
Those miners make up nearly half of the entire hash rate of the network. If the SPV miners and BU miners began building on the invalid block, then there would be two branches that are just about the same length.
And the moment that the valid chain was 1 block longer than the invalid chain, all miners would abandon the invalid chain. It might even happen sooner if people looked at what was happening and realized they were wasting time and resources. Either way, it wouldn't have any real effect on the valid chain.
As we have seen in the July 2015 fork, the SPV miners could accidentally cause this to happen.
And they deserve to waste their time and resources on an invalid chain if they are dumb enough to mine on it. It won't matter to me or anyone else on the valid chain. Why should we care?
One chain would probably die off once the human operators got involved as happened with the July 2015 fork eventually, one way or another.
Fixed that for you.
Now those miners should have learned from the July 2015 fork that SPV mining can be problematic, but I don't think any of them have stopped doing SPV mining.
Then they are foolish. A fool and his money are soon parted. That's the way bitcoin (And the world) works.
It really all depends on how their validation systems work, but such a scenario is entirely possible as we have seen in the past.
A scenario where foolish people waste time and resources on a foolis endeavor? Sure, it has happened throughout all of human history. It isn't going to stop anytime soon.