It's not just a wild speculation. The thing is that, yes, languages borrow words, especially Wanderworts related to new technological devices (e.g. "computer", "smartphone"). But the difference between a widespread borrowing and a native word is that when it's a later loanword it comes together with all the sound rules expected for that source language where it came from. They borrow the word as it's spoken by foreigners, not as they would pronounce it if that word had already existed in their language since the beginning. Speakers don't borrow it and remember to apply all the sound rules that determined the phonetic evolution of their own language for centuries and even milennia before they adopted that word. So, you almost always can distinguish quite well if a word is a later loanword or a native language that underwent a regualr phonetic evolution during the history of the language. It's not just a baseless assumption.