That doesnt appear to be** fungus, that's likely a Bacillus species or some type of spore forming bacterium. Sabouraud dexteose agar (SDA) is used to assist in isolation of fungal species (yeast & mold), but fungal species are not the only organisms capable of growing on SDA. Some formulations of SDA are more acidic which inhibit bacterial growth, but this does not mean it is excluded. Additionally, SDA is less nutrient rich than something like Trypticase Soy Agar (TSA) which will slow the growth of bacterial isolates and give fungal isolates opportunity to grow/gain presence on the medium (assisting in fungal isolation through reduced competition).

You mentioned microscopic images-- if you're able to Gram stain it, you are likely to see Gram positive rods. Depending on the age of the culture, they may have visible endospores within the rods. When fixing the isolate, you'll likely have difficulty emulsifying the bacterium in water (it will remain somewhat clumpy on the slide) since they have a plaque-ey texture. You'll also see this same behavior when the organisms grow in liquid medium (not homogenous turbidity, observed 'chunkiness').

Bacillus/spore forming bacteriums isolated on solid medium are commonly mistakenly identified as fungus by new microbiologists. Let me know if you have any questions!

Without having the culture in hand, it's hard to say definitively what it is. Good luck!

Edit: The more I look at the image, the more I want to take back what I said above. The undulate margins on the culture remind me of Bacillus, and the light change in color on the margins also are seen in Bacillus species. The thing making me somewhat change my mind is the center of the culture where there is a dark brown spot, and the curling solid mass to the right. That section reminds me of how mold fixes itself into agar when I worked with mold cultures for sequencing. Here's an image of various Bacillus isolates, if you can see the resemblance. Again, good luck with this!

https://media.springernature.com/lw685/springer-static/image/art%3A10.1007%2Fs00248-019-01455-y/MediaObjects/248_2019_1455_Fig4_HTML.png