Files are .WAV files with a .MP3 extension.
Interesting. I would say that observable file size (compared with play duration) is more indicative of a compressed format than of wav.
But I agree that something may be wrong (or at least unusual) in file format. This is what MediaInfo tells.
General
Complete name : 0033.mp3
Format : Wave
Format settings : WaveFormatEx
File size : 1.61 MiB
Duration : 2 min 0 s
Overall bit rate mode : Constant
Overall bit rate : 112 kb/s
FileExtension_Invalid : act at9 wav
Audio
Format : MPEG Audio
Format version : Version 1
Format profile : Layer 3
Format settings : Joint stereo / MS Stereo
Codec ID : 55
Codec ID/Hint : MP3
Duration : 2 min 0 s
Bit rate mode : Constant
Bit rate : 112 kb/s
Channel(s) : 2 channels
Sampling rate : 44.1 kHz
Compression mode : Lossy
Stream size : 1.61 MiB (100%)
It shows general format as Wave, but then Audio format as mp3. I am not an expert in audio formats. Maybe wave is a container format allowing different encodings ?