I am equally as sceptical about the 75% of entire force, however I am also very sceptical about their initial manpower numbers - e.g. actual troop numbers.I think the man might be misquoted.
They have +- 150.000 men on the ground. According to estimates the Russian army has the following personnel (without reserves)
Currently, there are 136 battalion tactical groups in the armed forces formed by contractors. The number of conscripts amounts to 225,000 and the number of contractors amounts to 405,000 as of March 2020 and exceeds the number of conscripts by 2 times as of the end of 2021.[52][53][54]
So it's 20-25 percent of the total armed forces. The Pentagon also confirmed (a direct contradiction of British intelligence) that they're not looking to reinforce their numbers right now.
We all know about Russian kleptocracy, so it wouldn't be on the realms of imagination that the numbers stated, linked to pay and equipment, may be embellished.
I know a fair few BA troops who are nominally 'full time' in support roles, but they're much closer to the reserve regardless of what the numbers may say.