His mewing softly was him telling you, "Thank You".
Thanking you for the 19 years of love and care that you had given him. Thanking you, for not putting him through any more tests. Thanking you, for holding him and being there for him while he passed on to RB.

You and your hubby have my deepest sympathies on the loss of your precious Pep.
May the loving memories comfort you and help you overcome the pain.

Rest in Peace dear Pep.