‘ And they said to him, “Your servants are come from a very far country because of the name of YHWH your God, for we have heard the fame of him, and all that he did in Egypt, and all that he did to the two kings of the Amorites, who were in Beyond Jordan, to Sihon king of Heshbon, and to Og king of Bashan, which was at Ashtaroth. ” '
Their claim was that they lived in a far country and had come because they knew the reputation of YHWH and wanted to be in alliance with His people. The suggestion was that they too wanted to know YHWH. Joshua knew that Israel was to be a kingdom of priests ministering to the nations (Exodus 19:6). We can therefore understand why he found the idea here tempting. We can often be so eager to do spiritual service that we forego caution.
Compare on this verse Rahab's description of the same incidents in Joshua 2:10. For Ashtaroth see Joshua 12:4. For Egypt see Exodus 1-15. For the defeat of the two kings mentioned see Numbers 21:21-35. Their subtlety comes out in that they made no mention of Jericho or Ai. That would not have had time to filter through to a far country.