Your friend isn't confused. In most states a manufactured home that hasn't been converted to real property is titled much like a vehicle, through the motor vehicle agency or a manufactured housing division, and there is a separate license category for people in the business of selling them, usually called a retailer or dealer license. The threshold that makes you a dealer, and whether an exemption covers homes you already own and have been renting, is set state by state, so that specific question goes to a lawyer or the state agency in the state the park sits in. Some states exempt occasional sales of your own inventory, some count as few as two or three sales in a year.
A park-owned home is usually shortened to POH, and a home the resident owns is a TOH, tenant-owned. Moving from POH to TOH is the direction most owners want, because the resident then carries the repairs and you're back to collecting lot rent on land you own.
The part that catches people is financing. If you sell for cash and hand over the title, it's a sale. If you carry paper so the resident pays you monthly, you may be originating a consumer loan on a dwelling, and there's a whole federal and state licensing layer around that which needs a licensed professional to look at your specific plan. Also confirm whether your state charges sales or use tax on the transfer, and get the title lien status checked before you agree on a price.
