in ipad air 2 a 1566, can only touch screen be replaced?

No he is correct. Unlike other models, Apple fused the LCD and top glass or digitizer together as one piece. There are companies that refurbish the broken glass but most repair shops like the one you went to will do a full screen assembly because we don’t have the special tools and equipment to replace just the glass. He might have a supplier that can refurbish that exact screen but it’s going to take a while because they have to take your screen off without damaging the LCD, then ship it to the company to refurb it, then ship it back so the technician can reinstall it. That’s also why we do a complete screen replacement because of a much faster turn around time.