All the season-ticket money, including premium seats and boxes have already been sold even if not paid for. And spending money like that is pretty standard. Club should have a decent idea of how much they will make from food and beer for instance. Every match should be sold out next season, so they can also calculate how much extra ticket money they get.

Also, I'm pretty sure they have a good idea about how many non-footballing events there will be next season as organizers have been in contact by now.

Plus I bet they are quite far in many sponsorship deals but sponsors want maximum visibility so this is not a good time to release them.

Spending before having the money is normal. Think of, say, an amusement park who buys a new ride. They don't necessarily have the money in the bank, instead they make predictions on how much the new ride would bring in money and borrow the purchase price.

And this is pretty much how most clubs in PL operate. They don't have the money in the bank in the summer but they have an idea of their revenue for that season. Sometimes (quite often) it's far too optimistic.