Steelpushing on metalminds?

[Ink and Embers Any pronouns]

In Bands of Mourning, we see that it's impossible to allomatically Push (and presumably also Pull) on metalminds, which is

Spoiler

how they identified the Bands to begin with, thinking they were aluminium. This seems to be a relatively well-known fact about metalminds, as the characters conclude they've found the Bands fairly quickly.

However, at the end of the Well of Ascension, Marsh attacks Sazed by Pushing Sazed's bag of metalminds into him, meaning he's able to heal using gold.

Why? Is it because Marsh was using Hemalurgy that he was able to Push on metalminds? Is it a special property of the Bands? Is it something else?

(As an aside, the reason I initially joined the Shard was to ask this, and I have consistently forgotten to do so for eleven months.)

[Aeoryi she/her]

Marsh's ability appears to be extremely strong when compared to the small amount of things likely stored in the metalmind to begin with; the Bands are likely filled to the brim with whatever it is that they're filled with and thus resist steelpushing more