The issue of "offering" vs "donation"... again

Due to our church deficit, the treasurer had a brief sharing during the service yesterday. He encouraged brothers and sisters to offer more because a lot of people left the church and he does need the money in the account so that he can write the cheques. Everything he said is ok until one thing came up. He told us that even someone outside (not a member of the congregation) donated $500 and we really need to work harder. He didn't say this in a negative way since he just wanted to encourage others. Of course, I don't know whether this person is a Christian or not. I hope she is. If not, this would be a big problem. "Donating" and "offering" are two completely different things. If we accepted it, this would give an impression to non-Christians that "offering" is another form of「添香油」. I've listened to other friends (who are not Christians) saying that when they go to church they need to donate money which they do not really want to. I'm sort of surprised that no one ever told them they do not need to because "offering" is only for people who believe. It doesn't make any sense if they're offering to a God whom they do not believe that exists. Addressing this issue is always important...