No, it's a capital repayment of a loan.
The only tax implication is that the €200k interest free loan would be deemed to be a gift of interest from the parents to the son at 1% or €2,000, so it would be subject to CAT, but would fall below the €3,000 annual small gift allowance.
So no tax implications at all if the house is worth €200k.
If the house is worth €800k, the gift would be €8k which would use up part of the parent to child CAT threshold. So, in practice, no tax implications either.
Brendan