Personally I think it's healthy to be sceptical about anything unusual coming out of both sides. Ukraine has claimed on a number of occasions that thermobaric weapons have been used, the latest was just yesterday, but never stating where or how they have been used, that hasn't been widely reported, because clearly media outlets have been sceptical.
Suddenly reports of their use became widespread yesterday, because the UK claimed that the Russian MoD had confirmed their use, without any indication of where or how this confirmation was made, or any information of where they had been used.
NATO doesn't seem to have claimed they have been used, and the US has actually said they have no evidence of their use, which is odd considering intelligence is shared between the UK & US.
It is, of course, possible there was a cock-up by our MoD quoting Ukraine's MoD and mistakenly labelled it as being the Russian MoD, especially as there doesn't seem to be any logic or advantage to the Russians admitting their use.