No, they mean rye berries typically: the whole grain; perhaps bought on a farmer's market?
And such grains by the way you should soak overnight in a bucket of water first before sterilizing to germinate endospores which are otherwise hard to kill by boiling. The fact that this is missing from this tek is not a good sign. Maybe go over to the Shroomery website and browse various of their teks.
Using something like the rye flour should be possible though but it would be a whole different 'tek', namely pretty much PF tek with vermiculite for an airy substrate and the rye flour to substitute for brown rice flour. The reason you want these brown/dark flours is because they use the whole grains and the husks (--> bran etc) are high in nutrients like protein while the main part of the [white] grain itself contains mostly carbohydrates for energetic value.
You can't just use any flour without the vermiculite though - with water flour just makes a paste and your substrate must be airy. Using whole grain berries is airy, there is plenty air in between them already. With flour the vermiculite you add which is an inert mineral of sorts gives it structure and surface area (lots of cavities).
So, conditions for the substrate are: it must contain an energy source, you also want nutrients like protein / amino acids / trace elements such as found in many vitamin pills (though don't add those lol) and preferably a source of sulfate among a few other things. The latter is usually not added by beginners as you can get away with just having those nutrients in other ingredients to some extent (like just the whole grain berries). But, sometimes things like bran, spent coffee grounds or gypsum are added depending on the substrate.
The substrate must also contain enough water (by sterilizing whole grains in water or adding enough to other substrate types until you have what is called field capacity). And the substrate must also be airy.
Ideally learn so you understand why everything is used and done the way it's done in these teks (they share commonalities if you get that)..
About your tek: you could find rye berries elsewhere like a farmer's market or find vermiculite at perhaps also that farmer's market or garden center and go the PF tek which makes cakes (clumped together mycelium) instead of colonized grains. I have grown on certain bird seed mixes but you shouldn't just use any seed mix - avoid sunflower seeds and make sure they are relatively big seeds, maybe check online or ask first before you go in that direction.
An advantage of grains is that you can loosen them up even if colonized, a PF style cake must be colonized inside untapered jars (no 'shoulder' on the jars but lids as wide as any other part of the jar), otherwise you can't get it out of the jar when it has clumped up. The grains should be spawned to bulk substrate but this is typically not for the total beginner.
An advantage of cakes is that once colonized they are less sensitive to contamination since they are already a clumped and closed unit that is good to go for fruiting.
What kind of jars / containers do you have? Or filter bags? etc And what kind of fruiting chamber? I take it you are a total beginner? The equipment you have and the plan you have do matter for choosing your substrate.
Let me know and i'll try to help.
