"After Many Years From 1901 to 1909 Prof. C. W. Irwin acted as principal of the Avondale School; and in his report to the General Conference of 1909 he bore witness of the fulfillment of that which had been said would come to pass on the Avondale estate, as follows: LS 376"
Both passages speak of the fulfillment of promises or predictions. Joshua 21:45 is a general statement about God's faithfulness to Israel, while the EGW passage refers to the fulfillment of specific prophecies regarding the Avondale estate. The connection is thematic, focusing on the idea of divine promises being realized.