Yeah, I think this is the most common, given by the era Bitcoin started going mainstream and the more popular. It was a time where Ponzi schemes did rock and people didn’t know much about it or how to differentiate between them both. Up till today, there are those who still don’t see Bitcoin to be no different from a Ponzi scheme. You don’t get to blame them much on this though, they are just ignorant and aren’t ready to make any smart moves about it.
I don't know how come people started tagging Bitcoin with Ponzi schemes, whether it was from the massive profit it gave over time or misinformation which someone forcefully spread based on what they feel about Bitcoin, which made the concept start spreading. In addition to that, I could also say I can remember very well that there were crashed Ponzi schemes whose major method of payment was Bitcoin, which those who don't understand that it was just used just like every other currency could use in that manner linked to Ponzi schemes.