> I imagine this will get them in some sort of trouble.

I'm not sure about this.

I bet Google is happy to collect the text data of up to 500 million users with zero restrictions from Telegram's end on how the data is used. I'm not a lawyer, but my hunch is that Google's data privacy policy applies to the official, premium service: https://cloud.google.com/terms/data-processing-terms

Google might make the determination that they'll get more value from allowing Telegram to abuse the unofficial API. However, they might face some angry customers who are paying a premium to use the official API now that this loophole has been published.