You may disagree with Fred's take on the reason behind Tesla's inclusion of the Model Y to the referral program, but your suggestion also doesn't really add up with the news from yesterday -- the leaked email from Elon.
So we have a situation where:
1. Elon informs his manufacturing team that the Model Y production needs to ramp up and the number of rectifications needs to be minimised, which indicates they're not where they want to be in terms of production rate, and
2. The Model Y is added to the referral program, indicating that the current rate of demand -- at least on the West Coast, given we're currently quite late in the quarter -- is below the production rate.
Weak demand is a reasonable conclusion. It may not be the correct one, but it is reasonable based on what we know. Again, it may simply be weak demand for the specific Model Y version (incl. wheels, body color) they're producing now, in the geography in which they have a good chance of delivering this quarter, but it's not completely unreasonable. People are just now starting to get back to work in many cases, some people may still need to figure out if there is a job waiting for them at the end of the lockdown, and so financial concerns are a major factor for many families; as such, it's possible some reservations are not transformed into orders right away.