First of all, you have to download the virus, which only auto-downloads if 1) you're on Chrome, which has auto-downloading turned on by default, 2) you're on the home page, and 3) you refresh the page from when you had it last open, presumably before the DNS hijack
Second of all, you'd have to actually run the .exe before it would affect your system; people who downloaded the file but deleted it without opening it seem to be fine
Also, as a third point, I think the Crunchyroll site is just flat down at this point(not that I'm going to go check, but so people say), so there isn't access to the virus anyway
So yes, take precautions, but I don't think having had a Crunchyroll tab open or re-connecting to the internet while you have a Crunchyroll tab open is going to put you at risk
for chrome users: there's an extension called the great suspender that will suspend tabs after a selected amount of time so that they don't eat up memory. upon opening chrome, it will retain the suspended status on any tabs that were suspended when closed. not really beneficial right now, but useful in the future.
for firefox/waterfox/pale moon/etc. users: I've been using this extension for other reasons for so long that I don't know if the browsers autoload tabs when you reopen, but tab mix plus has a setting where tabs only load when you select that tab if you have more than a selected number of tabs.
ETA: Crunchyroll has given the all clear