The summary of this bill is misleading. In fact, the bill only applies to rental transactions, *not* credit transactions in general. In fact, mortgage transactions are specifically excluded from the bill.
The idea of the bill is that landlords shouldn't be able discriminate against a tenant because they get money from disability, social security, section 8, or any other lawful source. Landlords would of course still be able to screen tenants for credit, background, income qualification, etc. They'd just have to treat all legal income as equivalent. Nothing to do with lending or mortgages at all.
And yes, discrimination on this basis is a real problem. Discrimination against Section 8 voucher-holders, for example, is shockingly common. Just search craigslist for "no section 8" for a small sampling.