The club didn't say who had done the valuation, but it's almost certainly been done as part of the annual accounts; as the player values would normally be amortised as part of the accounting procedure.
The players arent stated at fair value in the accounts, at least not in last year’s. they use the initial cost, transfer fees plus signing on fees and other acquisition costs, and write them off over the term of the contract. Maybe they’re changing policy this year and showing them at current value.
The player valuations are not the same as the value of the club. They are merely estimated sale values for each player. In reality no club is going to sell its entire playing staff.