Would have also learnt from the Colwill deal to have a future fee optionI'd imagine it's a loan with an option to buy.
Brighton aren't generally in the business of developing young players for other teams - they made an exception to bring in Colwill as part of the deal which took Cucurella to Chelsea, but have since been stung by Chelsea's refusal to negotiate a permanent deal.
A loan with a view to a permanent deal, including a buy back and sell on clause for us, seems most likely to me.