No, it was certainly malted. But there was also a lot of variation in brown malt, and the fuel used by different malting houses probably had a big influence. It was almost certainly not as dark, either. Pale malt started getting more and more common, and even though it was more expensive it had such a better yield than brown and amber malt that it became a larger portion of the grist. Therefore the brown malt had to be kilned darker to keep the same final color in the wort. With the darker kilning, the enzymes were destroyed.
Chances are that the lower yield was due to the higher kilning temperature breaking down some enzymes. It would be a fun project to figure out how long to toast some pale malt to the point where it will convert, but still provide appropriate color and flavor for a porter. I’ve made brown malt from toasting maris otter in the oven, and the aroma from it is fantastic! Might be a good project for this winter… toast the malt to a lighter color, use it for 100% of the grist, and if it doesn’t convert toss in some base malt to get the party going.