Why does as character return an integer on a list of dates

Question

I was surpirsed to see R do the following behaviour:

as.character(c(Sys.Date()))

#> [1] "2018-02-05"

as.character(list(Sys.Date()))

#> [1] "17567"

What causes this to occur? That is, clearly the "17567" is the result of as.integer(Sys.Date), but I do not follow the logic for why as.character(list(Sys.Date())) should wind up invoking as.integer().