밑밥 is like ... to lay the ground work I don't mean they are actually doing it. In terms of the meaning, the ground supports you to achieve good results. But it is usually negative as it sounds like nobodys think that it is good but you give your opinion that it is good to support psychologically. You can also think it can mean to try to take advantages For example, when you play a game you pretend that you are not good by saying it then your friend wouldnot do the best lol Also, when staff say to customers that the product is good for health or something like that even if it hasn't proved He just does it to support the product to sell it

밑밥's original meaning is a kind of bait in fishing. It means the food you throw into the water to attract fish to the area. It also commonly refers to something people offer as a bait to push their agenda for attaining something bigger, usually in a bad sense. For example, we say XX 회원으로 행세하며 밑밥을 깔았다 or XX 멤버라는 밑밥을 깔았다 (They (falsely) acted like members of XX as a ploy). So 그림에 조금씩 관심이 생겼다는 밑밥 probably means "a ploy/pretext that they got interested in painting", implying someone is using an interest in painting (which may not be true) as a bait to get something else they want (like getting a painter interested in them, for example). The person who said or wrote it saw through the ploy, because he or she wouldn't use the negative term 밑밥 otherwise.

I'm not Korean at all, but I think it could be "meat" rice, or a meal with meat. I don't know if that makes sense at all!