There's a lot of 'That depends...' when it comes to fuse ratings; for instance, a tardy porcelain fuse of the kind used domestically in Scandinavian countries until fairly recently were rated to take 90% over rated load for 1hr before melting; they were basically only going to provide short circuit protection.
Depending on the category of fuse and the time it held at a lower current before ramping it up to 400%, it may have operated as intended.
(Squinting at the C type trip diagram in my fuse box, it appears the fuse will withstand 2x rated load for 6 seconds before tripping, 4x for 1.5 seconds or so.)
