It is an APNG file. The main image (fallback) is green and the animation frame is yellow. Chrome doesn't handle the APNG chunks so it falls back on the main image. Here is a chunk listing; the acTL identifies it as an APNG.
# pngcheck -v *.png
File: BeMshNt.png (795 bytes)
chunk IHDR at offset 0x0000c, length 13
400 x 200 image, 8-bit palette, non-interlaced
chunk acTL at offset 0x00025, length 8
unknown private, ancillary, unsafe-to-copy chunk
chunk PLTE at offset 0x00039, length 9: 3 palette entries
chunk tRNS at offset 0x0004e, length 1: 1 transparency entry
chunk IDAT at offset 0x0005b, length 295
zlib: deflated, 32K window, maximum compression
chunk fcTL at offset 0x0018e, length 26
unknown private, ancillary, unsafe-to-copy chunk
chunk fdAT at offset 0x001b4, length 300
unknown private, ancillary, unsafe-to-copy chunk
chunk tEXt at offset 0x002ec, length 27, keyword: Software
chunk IEND at offset 0x00313, length 0
No errors detected in BeMshNt.png (9 chunks, 99.0% compression).