The case largely has to do with how technologically and industrially advanced Czechoslovakia was compared to Eastern European states and how seriously she took her army compared to Western European ones.
The Bren gun, the main striking force of British and Commonwealth infantry sections, was of Czechoslovak design; it has already been noted how well the Czech army was equipped in '38 with variants of the same. Tank production at the time, while certainly not nearly Germany's equal, produced technologically
advanced types in greater numbers than any non-major power (AFAIK, happy to be proven wrong, but I believe that the cca. 300 LT vz. 35 are first, followed by cca. 150 Polish 7TP built by about a year later). Modern estimates of countries'
real GDP place Czechoslovakia around the level of Belgium or the Netherlands, with an economy around twice as large as Hungary or Austria. Poland's economy (GDP) was bigger, of course, but also far less industrialised. I've heard claims of a UN ranking of countries by inter-war industrial output placing Czechoslovakia at 10th globally (I suppose the first 9 would be USA, GBR, GER, FRA, SOV, JAP, ITA, NED, BEL, in some order), although I can't find that reference. It would not surprise me if this were true--Bohemia inherited most Austro-Hungarian industry and experienced an industrial boom in the 20s after following trade-oriented policies at a time when others looked to autarky (and was accordingly hit disproportionately hard by the Great Depression, but the net effect was still overwhelmingly positive). So, compared to her neighbours, Czechoslovakia was an industrial powerhouse. Compared to the economically (and industrially) superior Low Countries, her industry had a far greater military orientation; hence the tank production etc.
And when it came time to mobilise in 1938, it's already been pointed out that she fielded a force of perhaps a million men, as numerous as the Polish army in 1939 (the difference being that the Czech mobilisation was completed before hostilities began, and that the Polish faced 1.5 million Germans to the Czechs' 1 million, but I digress back to Munich). To contrast that with the Hungarian army (for no particular reason), it comprised a total of seven brigades, 35k men, with an eighth added in 1939, and its invasion force for Slovakia in 1939 was counted in battalions, not divisions.
So, of what should this convince us? My conclusion is that Czechoslovakia was a minor power, but with emphasis on power. Ignoring its strengths compared to other non-major nations does the game a disservice.