That is pretty weird behaviour for the search term ‘BTC’. If you perform a side by side comparison to the term ‘Bitcoin’ (which has always shown more results than BTC), google trends places the interest for BTC in a 100:6 relation, which seems clearly wrong.

Adding and deleting comparison terms throws errors pretty often now, so it looks like of data error from the 31st of August onwards, setting the whole chart off-scale.

Edit: I’ve looked around and some refer to it as spam queries on Google, probably in an attempt to manipulate the price by affecting bots that may consult this parameter