Elsewhere in the thread he says the following. I have corrected some typos and added emphasis.

• I expect a firestorm of complaining over the use of the word `stack'. Maybe I'll be pleasantly surprised. I prefer to use such metaphors because I think such abstractions give people a useful handhold when they are coming from other backgrounds. I get jumped on a lot for using a stack metaphor when talking about Scheme because people apparently think I've forgotten that it's not a strict stack; personally, I think the people who are so quick to jump on me have forgotten that even a metaphor that has a flaw can be a powerful way to reason and express even when not speaking rigorously. The remark here is intended to allow someone who is just barely reading along to confirm that something he may have strong knowledge of in another domain is in fact what is being discussed here. To not offer that handhold seems to me to be impolite.