737 approach procedure
There have been a few 737 low speed on approach events over the last few years (eg Thomson at bournemouth, circling at BOD) This may or may not be a factor in this.
Up till a few years ago, the Boeing procedure when flying manually on approach was to call for " speed off" (pushing the speed switch on the MCP) so the autothrottle no longer actively controlled thrust but was available in case of go around and provided low speed protection ( a bit like alpha floor on the bus)
This was changed, recommending having it completely disarmed (I believe because of unwanted autothrottle during the flare)
Perhaps this should be reviewed possibly clicking it out totally as thrust is reduced in the flare?