Really I just set out to investigate this slide, and associated commentary:
The implication is that A) it's something other than a hairdryer burn, and B) it's related to a UFO sighting 9 months later. The claim is Vallee's. We don't know what the witness here claims about the link. She did not think she burnt herself and suspected the mark was related to meditation.
I think the investigation in this thread is sufficient to show this is a hairdryer burn and probably an accidental one she does not remember.
I agree the investigation in this thread is more than sufficient to show it's a hairdryer burn. But it's insufficient to establish that it's "probably an accidental one she does not remember". Since she didn't think she burnt herself but rather attributed it to meditation (an extraordinary claim), while sending the picture to a known ufologist to investigate (a notorious author of extraordinary claims), to just believe it as "probable" she genuinely forgot seems a tad too trusting to me. It's just as possible she either lied to get attention or she's delusional about a great many things, including her lack of burn memories. All three hypotheses are possible (including of course the accidental-but-forgotten-burn hypothesis). Plus a combination of them (eg. an accidental burn but delusionally selective / lying about her memories of burning herself).
I went back and looked again, and there are some references to aliens, often joking.
If you're referring to this thread (https://www.ufologie-paranormal.org/t13539-etranges-traces-circulaires-cutanees), it doesn't matter imo how many of the posters explicitly refer to aliens. The whole thread is a ufology/paranormal thread. To upload a burn mark there carries the reasonable default assumption that the poster (1) seeks some kind of emotional payoff from people thinking it is possibly an alien marking or, alternatively, (2) is delusionally ready to believe it's one. As such, the likelihood goes up that the person's claim of not remembering the burn is also suspect or delusionally selective/psychotic.
The reports on this American thread (you also posted) seem like a number of genuinely gullible/delusional people plus one attention-seeker (the one posting a breast pic). But I admit I'm no psychology expert. But neither is anyone else posting on this thread.