It’s probably the signing bonus, base pay for an E-1 is much lower. Going off 2023 rates the first year base pay comes out to $22,432.80 plus BAH/S, specialty pay etc. might bring it up to $30k ish. Even if they are coming in as an E-4 base pay will be $30,042.
There are absolutely jobs that have a 35k sign on bonus. Or did at least. The way the OP is worded would be strange for it to be base pay. Sounds like a bonus to me. But you can think what you want.